With the ever increasing utilization of computers and computer systems for seemingly unending applications in various technological fields, it has become increasingly important to provide chassis or housings for computer components which will withstand severe environmental conditions. The problem has been long recognized in the aircraft industry, for example, and is becoming increasingly important with respect to other vehicular applications, particularly land vehicles. Generally speaking, environmental conditions will be most severe for military vehicles such as tanks, armored personnel carriers and the like which are required to perform under widely diverse climatic conditions but also severe operational conditions, i.e., conditions attendant to the specialized function of the vehicles. For computer and other electronic components, it is critical that such components be constructed, supported and enclosed in such a way as to be able to withstand such conditions including maximum extremes of shock, vibration, temperature, EMI, humidity, fungus as well as sand/dust, etc.
It is the principal object of the present invention to provide a versatile, compact, lightweight VME bus system which is low in cost, compact, versatile and lightweight, but which also meets the most rigorous environmental and electromagnetic military standards. Significantly, no external shock or vibration isolation is required by reason of the highly rigid nature of the construction. The present invention also incorporates modular construction, ease of repair and low maintenance.
Thus, in one exemplary embodiment of the invention, a computer chassis construction is provided which has a basic box-like configuration including aluminum alloy top and bottom walls or covers, a pair of side walls or plates and a pair of end plates rigidly fastened together as a rectangular enclosure.
A conventional backplane is rigidly mounted within the enclosure, adjacent the bottom cover. The backplane is provided with a plurality of connectors for supporting a plurality of thin, commercially available circuit cards (five in a preferred embodiment) in substantially parallel, upright relationship. The backplane also supports the power supply which is located behind one of the end plates, referred to herein as the face plate which is at the "front" of the enclosure. The other end plate is at the "rear" of the enclosure. As a result, the enclosure is divided into a circuit supporting area and a power supply supporting area by means of an interior partition rigidly mounted between the side plates and extending generally between the top and bottom of the enclosure.
The interior partition, also constructed of aluminum alloy material, has a first plurality of parallel, elongated grooves machined therein so as to extend substantially parallel to the side plates of the enclosure.
A similarly configured second plurality of grooves are machined in the interior surface of the end plate opposite the face plate, such that the first and second sets of grooves face each other within the circuit card supporting area of the enclosure.
The first and second sets of grooves (five in each set in accordance with the preferred embodiment) are designed to receive opposite parallel edges (referred to here as second and third edges) of the circuit cards mounted on the backplane, (the edge of each card electrically connected along the backplane will be referred to herein as the first edge). In order to rigidify the cards within the opposed grooves, commercially available, expandable locking bars, sold under the name Wedge-Lok.TM. (Series 40-5 or 40-5P), manufactured by EG&G Birtcher Co. of El Monte, California, are utilized, one along each of the second and third edges of each card. The locking fins rigidly clamp the second and third edges of the cards against adjacent groove sidewalls.
A card comb is rigidly secured to the interior surface of the top cover, and extends transversely of the top cover, between the forward and rearward ends thereof. The card comb is provided with a plurality (five in the preferred embodiment) slots, designed to receive portions of the fourth or top edges (opposite the first edges) of the circuit cards.
Upon assembly of the top cover to the end and side plates of the enclosure, the circuit cards will be rigidly and immovably secured within the circuit card supporting area of the enclosure.
Further rigidity and stiffening of the backplane (and card assembly) is achieved by transverse bars sandwiching the backplane and extending between the enclosure side plates, between the face plate and rear end plate. These bars are fastened to each other through the backplane, to the side plates, and to the bottom cover.
In the power supply supporting area of the enclosure, the power supply box is secured to the backplane via a voltage and I/O connector and to the interior partition separating the circuit supporting area from the power supply supporting area. The power supply is also operatively connected to the face plate which incorporates the various power, I/O connectors, indicators, etc. for the power supply.
It is another feature of this invention that no moving parts are required and, more particularly, no active cooling scheme is necessary. The circuit cards are in heat conducting relationship with the enclosure (rear) end plate which is provided on its exterior surface with a plurality of cooling fins, and to the interior partition which, in turn, is in heat conducting relationship with the enclosure side plates. The latter are also provided with cooling fins on their exterior surfaces.
In a similar manner, the power supply is in heat conducting relationship with the interior partition.
It is another feature of this invention that EMI protection is facilitated and enhanced by plating the surfaces of the side and end plates with thin layers of copper, nickel and tin, in that order.
It is still another feature of the invention that captive fasteners are employed to secure the top and bottom covers, side plates and end plates as described further herein, thereby minimizing the potential for losing the fasteners in the field during repair/replacement procedures.
The above described chassis construction thus incorporates the following features:
(1) the chassis is designed to house and power circuit cards for computer systems used in very severe environments, i.e., pre-specified maximum extremes of shock, vibration, temperature, EMI, humidity, fungus, as well as sand/dust environments;
(2) the chassis construction provides for the dissipation of circuit card heat by internal conduction, external convection and radiation from cooling fins;
(3) the chassis envelope meets the 11/2 1/2 ATR (Air Transport Rack) form factor (ARINC 404A Standard);
(4) the power supply is completely enclosed within and heat sink provided by the chassis;
(5) the chassis face plate provides an easy means to access and perform maintenance on the power supply and associated cabling and connectors;
(6) the chassis walls are processed with a multi-layer metal plating for enhanced EMI protection;
(7) the chassis top and bottom plates employ a specific type of captive fastener and fastener spacing to insure EMI integrity;
(8) the chassis design provides the internal means to insure rigid internal mounting of the power supply, backplane and circuit card assemblies;
(9) a card edge comb integral to the top plate is provided for insuring immobilization of the circuit card assemblies;
(10) the overall chassis construction design provides extreme stiffness of structure and immobilization of internal components to enhance the system's immunity to vibration. As a result, the system can be "hard mounted" directly in a land, sea or airborne platform without the need for shock mounting or external vibration isolation;
(11) the chassis has been tested and certified to the environmental specifications and testing procedures which are defined in MIL-STD-810D; and
(12) the chassis has been tested and certified to EMI immunity specifications which are defined in MIL Standard-461.
Other objects and advantages of the present invention will become apparent from the detailed description which follows.